328 Intelligence and Miscellaneous Articles. 



assumed. For this purpose two equal threads stretched vertically 

 by weights might be used, and a plane mirror without edge be so 

 adjusted that the reflected piece of the one thread falls in a straight 

 line with the directly seen parts of the other in each position of 

 the eye. 



After the position of the image produced by a plane mirror has 

 thus been fixed, the discovery of the position of other subjective 

 pictures will be possible by means of a transparent and at the same 

 time reflecting plane-parallel plate on which a luminous point is 

 reflected. The plate is to be so arranged that the reflected picture 

 of the luminous point covers a point of the image in question. An 

 assistant must move the luminous point until the reflected and re- 

 fracted image no longer move towards each other in any motion of 

 the eye. The directly measured distance of the reflected point from 

 the plane-parallel plate is equal to the required distance of the sub- 

 jective image produced by the optical apparatus from the same plate. 

 — Poggendorff s Annalen, vol. cxxiii. p. 655. 



ON A SIMPLIFIED METHOD OF EXTRACTING INDIUM FROM THE 

 FREIBERG ZINCBLENDES. BY M. WESELSKY. 



The roasted and levigated blendes are treated with a mixture of ten 

 parts of hydrochloric and one of nitric acids ; the solution, separated 

 from silica and the liberated sulphur, is greatly diluted with water, 

 and carbonate of soda added until a precipitate first begins to form. 

 The solution is boiled, hyposulphite^ of soda being added until no 

 more sulphurous acid escapes, and the precipitate, which at first is 

 yellowish and flocculent, has become black, w r hen it readily settles 

 down. The solution contains, besides all the iron and zinc, small 

 quantities of arsenic and copper, and also part of the indium. The 

 black precipitate consists of the sulphur- compounds of arsenic, lead, 

 copper, &c, and contains the rest of the indium. Without removing 

 it, freshty-precipitated carbonate of baryta in excess is added to the 

 liquid when it is cold, and the whole allowed to stand for twelve 

 hours. The precipitate, which, besides the above sulphides, contains 

 all the indium and the excess of carbonate of baryta, is well washed, 

 the air being excluded, and is then treated with dilute hydrochloric 

 acid. In this way the carbonate of baryta and the indium are dis- 

 solved. To remove a small quantity of sulphides which pass into 

 solution, sulphuretted hydrogen is passed into the acid solution ; and 

 baryta is removed by sulphuric acid. Oxide of indium is separated 

 from any possibly adhering oxides of iron or zinc by means of car- 

 bonate of baryta. 



From experiments with which M. Weselskyis at present occupied, 

 it appears that, under suitable circumstances, indium may be com- 

 pletely precipitated by hyposulphite^of soda, by which the applica- 

 tion of carbonate of baryta is quite avoided. — Bulletin der Akademie 

 in Wien, vol. vii. p. 1869. 



